<div dir="ltr"><div dir="ltr"><div><div dir="ltr" class="gmail_signature"><div dir="ltr"><br></div></div></div></div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Nov 14, 2022 at 8:05 PM Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr">mhyaqteen@sju.ac.kr</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg7674002052180736609">
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<p class="MsoNormal">I am sorry for the trouble but I don’t understand its usage. Like I want to read Vec xr. I am giving it to a pointer array. How would I access the values of the vector? Could you please briefly explain?</p></div></div></div></blockquote><div>Suppose you have a vector x with global size 10, and you run with 2 MPI ranks, then the code sketch would be</div><div><br></div>const PetscScalar *a;<br>VecGetArrayRead(x, &a);</div><div class="gmail_quote"> // code reading a[]. On rank 0, a[0]~[a4] contains x[0]~x[4]; on rank 1, a[0]~[a4] contains x[5]~x[9]</div><div class="gmail_quote">VecRestoreArrayRead(x, &a);<br><div><br></div><div>See manuals at <a href="https://petsc.org/release/docs/manualpages/Vec/VecGetArrayRead/">https://petsc.org/release/docs/manualpages/Vec/VecGetArrayRead/</a>, <a href="https://petsc.org/release/docs/manualpages/Vec/VecGetLocalSize/">https://petsc.org/release/docs/manualpages/Vec/VecGetLocalSize/</a>, and also examples there.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg7674002052180736609"><div lang="EN-US" style="overflow-wrap: break-word;"><div class="m_7674002052180736609WordSection1"><p class="MsoNormal">
<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><b>From:</b> Matthew Knepley <<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>> <br>
<b>Sent:</b> Tuesday, November 15, 2022 9:54 AM<br>
<b>To:</b> Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr" target="_blank">mhyaqteen@sju.ac.kr</a>><br>
<b>Cc:</b> <a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a><br>
<b>Subject:</b> Re: [petsc-users] Reading Vectors from a PETSc Vec<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">On Mon, Nov 14, 2022 at 7:50 PM Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr" target="_blank">mhyaqteen@sju.ac.kr</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">I am using Eigen library to which I have to write these vector values from PETSc Vec. tdof is the length of the vector that I need and ei is the number of value in as an
index:<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">PetscInt ei[tdof];<br>
PetscScalar eveci[tdof];<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">for (int i = 0; i < tdof; i++)<br>
ei[i] = i;<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">If you are running in serial, just use VecGetArrayRead().<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"> Thanks,<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"> Matt<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">if (nconv>0)
<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> {<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> eval.setZero(nconv);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> evec.setZero(KS.rows(),nconv);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(PetscPrintf(PETSC_COMM_WORLD,<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> " k ||Ax-kx||/||kx||\n"<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> " ----------------- ------------------\n"));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> for (int i = 0; i < nconv; i++)<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> {<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(EPSGetEigenpair(eps,i,&kr,&ki,xr,xi));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #if defined(PETSC_USE_COMPLEX)<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> re = PetscRealPart(kr);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> im = PetscImaginaryPart(kr);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #else<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> re = kr;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> im = ki;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #endif<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> if (im!=0.0) PetscCall(PetscPrintf(PETSC_COMM_WORLD," %9f%+9fi %12g\n",(double)re,(double)im,(double)error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> else PetscCall(PetscPrintf(PETSC_COMM_WORLD," %12f %12g\n",(double)re,(double)error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> eval(i) = re;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> VecGetValues(xr, tdof, ei, eveci);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> for (int j = 0; j < tdof; j++)<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> {<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> evec(j, i) = eveci[j];<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> }<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> }<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n"));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> }<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt;color:black">Thank you <u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt;color:black">Ali<u></u><u></u></span></p>
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<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> Matthew Knepley <<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>><br>
<b>Sent:</b> Tuesday, November 15, 2022 9:43 AM<br>
<b>To:</b> Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr" target="_blank">mhyaqteen@sju.ac.kr</a>><br>
<b>Cc:</b> <a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a> <<a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a>><br>
<b>Subject:</b> Re: [petsc-users] Reading Vectors from a PETSc Vec</span> <u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal">On Mon, Nov 14, 2022 at 7:39 PM Mohammad Ali Yaqteen <<a href="mailto:mhyaqteen@sju.ac.kr" target="_blank">mhyaqteen@sju.ac.kr</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">I am using the following procedure to read from Vec, but it keeps giving me the same values! I was told that using VecGetValues gives wrog output.
<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">By who? It does not give the wrong output.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">You do not show where in the code you define tdof and ei[].<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">If not this, then what function should be used to read the contents of a vector?<u></u><u></u></span></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">I think it would be simpler for you to use VecGetArrayRead(), unless you want values from other processes.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"> Thanks,<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"> Matt<u></u><u></u></p>
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<p class="MsoNormal"> <u></u><u></u></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">for (int i = 0; i < nconv; i++)
<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> {<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(EPSGetEigenpair(eps,i,&kr,&ki,xr,xi));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(EPSComputeError(eps,i,EPS_ERROR_RELATIVE,&error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #if defined(PETSC_USE_COMPLEX)<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> re = PetscRealPart(kr);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> im = PetscImaginaryPart(kr);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #else<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> re = kr;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> im = ki;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> #endif<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> if (im!=0.0) PetscCall(PetscPrintf(PETSC_COMM_WORLD," %9f%+9fi %12g\n",(double)re,(double)im,(double)error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> else PetscCall(PetscPrintf(PETSC_COMM_WORLD," %12f %12g\n",(double)re,(double)error1));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> eval(i) = re;<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> VecGetValues(xr, tdof, ei, eveci);<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> for (int j = 0; j < tdof; j++)<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> {<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> evec(j, i) = eveci[j];<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> }<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> }<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"> PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n"));<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">Thank you<u></u><u></u></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12pt;color:black">Ali<u></u><u></u></span></p>
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<p class="MsoNormal">-- <u></u><u></u></p>
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<p class="MsoNormal">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><u></u><u></u></p>
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<p class="MsoNormal">-- <u></u><u></u></p>
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<p class="MsoNormal">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><u></u><u></u></p>
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